This invention relates generally to improvements in molded plastic pipe components of the type typically found in irrigation sprinkler systems and the like. More specifically, this invention relates to an improved molded plastic elbow and to a related mold assembly and method for producing the elbow with an internal flow path defining a turn, wherein the inside edge of the turn is smoothly radiused for reduced hydraulic pressure loss and to provide the elbow with improved fatigue resistance.
Plastic pipe and related molded plastic pipe fittings are well known in the art for use in a variety of relatively low to mid-range fluid pressure applications, particularly such as in irrigation sprinkler systems to deliver irrigation water under pressure to sprinkler devices having appropriate spray nozzles or the like to distribute the water over a prescribed terrain area. In this regard, molded plastic pipe fittings such as elbow fittings and the like are used for interconnecting lengths of pipe at an angle, whereby such elbow fittings define an internal flow path extending through a turn, typically a 90° turn. In one common form used primarily to interconnect elongated pipe sections in an irrigation supply network, the elbow fitting is adapted for slip-fit adhesive connection to elongated pipe sections. In another common form, the elbow fitting may include one or more threaded segments to form a so-called swing joint or coupling for quick and easy threaded connection to adjacent pipe sections such as a riser pipe having a sprinkler device mounted at an upper end thereof.
In the past, molded plastic elbow fittings have been formed by injection molding processes wherein plastic material is injected under heat and pressure into a mold cavity defined by closed mold members. A pair of retractable core units are typically mounted to extend into the mold cavity in an angularly intersecting relation for cooperatively defining the internal flow path through the injection molded fitting, wherein these core units are adapted for sliding linear retraction from the molded part when the mold members are opened to release the molded part. Unfortunately, this standard molding apparatus and related process has necessarily limited the inside edge geometry of the internal flow path to a relatively sharp corner in order to permit interference-free linear retraction of the sliding core units from the molded part. This sharp-cornered geometry undesirably contributes to substantial hydraulic pressure loss as water flows through the elbow fitting. As a result, especially in an irrigation network including a substantial number of such elbow fittings, the cumulative pressure loss attributable to the elbow fittings can adversely restrict the terrain area which can be effectively irrigated. Moreover, the relatively sharp inside edge geometry represents a stress concentration site which is susceptible to fatigue cracking in response to on-off pressure cycling over a period of time.
Similarly, hydraulic pressure losses and fatigue problems have been noted in other molded plastic elbow-type fluid conduits, such as, for example, in the inlet and outlet portions of molded plastic valve bodies such as typical anti-syphon and pressure and flow regulating irrigation control valves. In these instances, the valve bodies are typically molded with elbow-shaped inlet and outlet conduit sections for slip-fit adhesive or threaded connections to elongated supply pipes, and like the elbow fittings just discussed, the elbow sections function to direct the incoming and outlet fluid flows through turns of typically 90° within the valve body.
There exists, therefore, a significant need for an improved molded plastic elbow and a related mold assembly and production method, wherein the elbow has an internal flow path defining a turn with a smoothly curved or smoothly radiused inside edge geometry, for reduced hydraulic pressure loss and improved fatigue resistance. The present invention fulfills these needs and provides further related advantages.